The present invention relates to a navigation system for guiding a user of a navigation apparatus from a current location to a destination and, more particularly to a communication navigation system wherein a navigation apparatus mounted on a vehicle receives a drive route to a destination from an information center or an external device by communication therebetween.
A navigation system has been widely used in a vehicle to provide a recommended route from a current location to a destination, along which a user of the system may drive the vehicle. The navigation system stores destination data, road link data and map data. The road link data is used for searching for a route from the current location to the destination. The current location of the vehicle is detected by a GPS receiver, for example. The systems refers to the current vehicle location and the searched route to guide the user by showing the direction which the user should head off or by giving instruction which roars the user should take, for example xe2x80x9cgo straightxe2x80x9d or xe2x80x9cturn at a crossing aheadxe2x80x9d.
Recently a communication navigation system has been developed, wherein a navigation apparatus mounted on a vehicle detects the current location and executes route guidance operation, whereas an information center, outside of the vehicle, searches a route to the destination and transmits the route to the navigation apparatus.
An example of the communication navigating system is proposed in Japanese patent laid-open publication No.10-160497 wherein an guiding route is determined by the navigation apparatus mounted on the vehicle based on the recommended route data which is prepared by the information center and transmitted therefrom to the navigation apparatus. In this system, the recommended route data comprises a series of index numbers, each index numbers can specify a particular road link from a road link database. Once the series of index numbers is transmitted to the navigation apparatus, the road links corresponding to the index numbers are extracted from a road links database in the navigation apparatus and guiding route data is generated by connecting the extracted road links. The system has the advantage of efficient data communication because of only transmitting a series of index numbers for road links along the recommended route instead of transmitting whole data for recommend route such as coordinates, street names and number of lanes etc,. those may be used for guiding the user along the route.
However, although the information center has the latest road links database, the navigation apparatus may not have a road link database same as in the information center.
Accordingly, the series of index numbers transmitted from the information center may include one or more index numbers specifying the road links which is only included in the latest version road link database in the information center but not in the road link database of an older version in the navigation apparatus. In such a case, the navigation apparatus is not able to determine a road link along the recommended route by using transmitted the series of the index numbers.
On the other hand, if the information center transmits whole data of recommended route, the user will owe high communication costs because of huge data volume for transmitting.
It is a primary object of the present invention to provide a novel communication navigation system which is capable of executing route guidance even if the road links data stored in the navigation apparatus mounted on the vehicle is of an older version than that stored in the information center without increasing communication costs.
To achieve the above objects, in accordance with an aspect of the present invention, there is provided a communication navigation system which includes an information center and at least one of navigation apparatuses, in which data concerning a recommended route from a current location of the navigation apparatus to a destination is transmitted from the information center to the navigation apparatus, and then route guidance is carried out in the navigation apparatus using the data transmitted from the navigation center, comprises:
the navigation apparatus of the communication navigation system having:
road information storage means which stores road information including at least road network data which is composed of data of plural road links, and identification data of the road information;
data transmitting means for transmitting at least data concerning a current location and a destination of the navigation apparatus and the identification data of the road information stored in the road information storage means to the information center;
data receiving means for receiving data concerning recommended route guidance information from the information center;
route guidance data generating means for generating route guidance data based on the road information stored in the road information storage means and based on the recommended route guidance information transmitted from the information center;
route guiding means for guiding a user of the navigation apparatus from the current location to the destination of the navigation apparatus using the route guidance data;
and the information center of the navigation system having:
database which stored road information including at least road network data which is composed of a plurality of road links and identification data of said road information;
data receiving means for receiving at least data concerning the current location and the destination of the navigation apparatus and the identification data of the road information stored in the road information storage means from the navigation apparatus;
recommended route determining means for determining recommended route, by extracting road links of the road network stored in the database, from the current location to the destination received from the navigation apparatus based on the road information stored in the database;
judging means for judging respectively whether or not each data of road links along the recommended is contained in the road information stored in the road information storage means in the navigation apparatus, by comparing the identification data transmitted from the navigation apparatus and the identification data of the road information stored in the database;
recommended route guidance information generating means for generating recommended route guidance information, based on the database, containing data which enable to specify the each data of the road links along the recommended route from the road information stored in the road information storage means in a case where the each data of the road links is considered to be contained in the road information storage means by the judging means, and data which enable to reconstruct the each data of the road links along the recommended route without the road information stored in the road information storage means in a case where the each data of the road links is considered not to be contained in the road information stored in the road information storage means by the judging means.
data transmitting means for transmitting said recommended route guidance information to the navigation apparatus.
In a preferred embodiment of the present invention, the route guidance data generating means, referring to transmitted data of the recommended route guidance information from the information center, further comprising:
(a) means for extracting data of road links, which is specified by the transmitted data enabling to specify the each data of the road links along the recommended route, from the road information stored in the road information stored means in the navigation apparatus,
(b) means for reconstructing data of road links by using the transmitted data enabling to reconstruct the each data of the road links along the recommended route,
and the route guidance data generating means uses the means of (a) and/or (b) for generating recommended route guidance information.
In an example of the above preferred embodiment, the road information stored in the road information storage means further including guidance data corresponding to the plurality of the road links, and the road information stored in the database further including guidance data corresponding to the plurality of the road links, and the recommended route guidance information further contains guidance data corresponding to the each data of the road links which is considered not to be contained in the road information stored in the road information storage means, and the route guidance data generating means generates route guidance data by further using the guidance data contained in the transmitted data of the recommended route guidance, and by further extracting guidance data, from the road information storage means, corresponding to the each data of the road links specified by the transmitted data of the recommended route guidance.
In this example, both of the guidance data stored in the road information storage means and the guidance data stored in the database contain at least one of:
data of a road length;
data of coordinates for drawing;
data of coordinates for matching a location of the navigation apparatus;
data of number of lanes; corresponding to the each road link.
In another preferred embodiment of the present invention, both of the identification data stored in the road information storage means and the identification data stored in the database are a version number of the road information, and the database has road information of all version, and the recommended route determining means determines the recommended route using road information of latest version stored in the database, and the judging means judges whether or not the each data of a road link along the recommended is contained in the road information stored in the road information storage means in the navigation apparatus, by comparing the version number of the latest road information being used for determining the recommended route and the version number transmitted from the navigation apparatus.
In still another preferred embodiment of the present invention, the identification data stored in the road information storage means is a version number of the road information, and the each data of the road links in the database contains a version number expressing a road information version at which the each data of the road links have been newly added for the road information and the judging means judges whether or not the each data of the road links along the recommended route is contained in the road information stored in the road information storage means in the navigation apparatus, by respectively comparing the version number of the each data of the road links and the version number transmitted from the navigation apparatus.
In still another preferred embodiment of the present invention, the information center further comprises external information acquisition means for acquiring latest traffic condition and/or latest road condition, and the recommended route determining means determines the recommended route from the current location to the destination of the navigation apparatus in consideration of the latest traffic condition and/or the latest road condition.
In still another preferred embodiment of the present invention, both of the data transmitting means and the data receiving means of the information center, and both of the data transmitting means and the data receiving means of the navigation apparatus are designed so as to communicate using packet switching technique and/or circuit switching technique.